C Primer CAS CS210 Ying Ye Boston University

Outline Hello, world Basics in C Comparison of C and Java

Getting started Open PuTTY, connect to csa2 In your terminal, type in:  cd ~/Desktop  wget  vim hello.c

Hello, world #include tells compiler to add a library(stdio) into the program Why? ==> printf() int main(void):  program begins executing from main  equivalent to main(), but more standard:  int main(void);  int main(int argc, char *argv[]);

Hello, world printf("hello, world\n") prints out the character string passed to it return 0:  return value required by main() function  some compilers(like gcc) can add "return 0" automatically if your main function doesn't return a value(only in main function)

Hello, world Type in: gcc hello.c Try: ls Run:./a.out Want to specify the name? Try: gcc -o XXX(name you like) hello.c e.g.gcc -o abc hello.c Try ls again

Basics in C Basic types DatatypeSizeRange char to 127 short to int 4-2,147,483,648 to 2,147,483,647 long 4-2,147,483,648 to 2,147,483,647 float 43.4*10 +/-38 double 81.7*10 +/-308 (In 32-bit machine!) Arrays

Basics in C Operators  Arithmetic:  ++, --  +, -, *, /, %  Relational:  >, =, ==, !=  Logical:  &&, ||, !  Bitwise:  &, |, ^, >, ~  Assignment:  =, +=, -=, *=, /=, %=, &=, ^=, |=, >=

Basics in C Control flow  if...else  switch  while  do...while  for  continue/break

Basics in C Functions  Definition: return-type function-name(parameter declarations) { declarations statements }  Note: If you want to use a function before you define it in the source code, you should declare the function before using it. Example: C textbook page 24

Basics in C  Call by value: void swap(int a, int b) {int c = a; a = b; b = c;} int main(void) {int x = 1, y = 2; swap(x, y); return 0; }

C and Java { for(int i = 0; i < 10; i++) printf("hello, world\n"); return 0; } Add an option in gcc: gcc -o XXX -std=c99 hello.c {int i; for(i = 0; i < 10; i++) printf("hello, world\n"); return 0; }

C and Java Uninitialized variables:  In Java: Instance variables initialized to 0, null, or false  In C: Initialized to random values No exceptions in C: return specific value to indicate error No string data type in C: use arrays to store character strings e.g. char name[5] = {'J', 'o', 'h', 'n', '\0'};

Macros  Definition: A macro is a fragment of code which has been given a name. Whenever the name is used, it is represented by the contents of the macro. #define macro_name contents_of_macro  Usages:  Define a number as a macro: #define TOTAL 100 int a = TOTAL;  Define a character string: #define NAME "John" printf(NAME);  Define a function: #define ADD(a, b) a += b int x = 1, y = 2;ADD(x, y);